Fiber optic communication systems include optical connectors that mate segments of optical fibers. The principal function of an optical fiber connector is to hold a fiber end such that the core of the fiber is axially aligned with the optical path of the fiber component, etc. to which the connector is mated, e.g., so that light from the one fiber is optically coupled to another. This is achieved by holding the end of the fiber such that the core of the fiber is axially aligned with the optical pathway of the mating fiber. By way of example, optical fibers may be mated at a splice, e.g., within a single connector, or may be mated between one or more connectors or optoelectronic devices.
To facilitate an effective optical coupling between a connector and another connector or other device, the end face of the connector's ferrule is typically polished. Preparing a polished ferrule is a sophisticated process. It requires cleaving the fibers, terminating them in a ferrule, and polishing the ferrule to exacting tolerances. Therefore, such a process is usually performed in a controlled setting with precision equipment by skilled personnel. Frequently, however, connectors must be terminated in the field where such facilities and personnel are not available. Under these conditions, it is desirable to omit the step of polishing the ferrule by instead splicing the field fiber to a fiber stub already terminated within a polished ferrule of a connector. Because the ferrule is already polished in a fiber-stub, field-installable connector, field installation requires only optically coupling the field fiber to the fiber stub by forming a splice therebetween.
Conventional technology involves perpendicular cleaving of the fiber ends to create a fiber end face that is substantially planar, and substantially normal to an axis of the fiber. The ends of the fibers are typically mated by introducing a refractive index-matched gel to improve optical coupling therebetween. The optical reflectance of such a joint is typically 40-60 dB under ambient temperature conditions, which is suitable for many optical communication applications. However, as the connector temperature departs from the ambient, the refractive index of the gel changes, which increases the reflectance at the splice. This increase can cause degradation of the optical signal, particularly when coherent light sources are used for signal propagation.
It has been found that improved optical connections can be made, with and without index matching gel, by mating fibers that have been prepared to have an angled end face, e.g., one that is substantially flat but that is not substantially perpendicular to the optical axis of the fiber. Various techniques and tools for providing an angled end face are well known in the art. Providing an angled end face tends to cause light reflected at the fiber interface to be reflected at an angle into the cladding of the fiber, rather than back down the fiber core where it can interfere and diminish forward-propagating optical signals. Such mating arrangements can therefore improve (increase) return loss, which is the ratio of input power to reflected power.
Though the advantages of angle cleaved fibers is well-known, conventional wisdom holds that in order to mate an angle cleaved fiber, the mating fiber must be similarly angle cleaved. Further, conventional wisdom holds that the angle-cleaved launch fiber must be rotationally aligned to mate with the angle-cleaved receive fiber (i.e., they must be rotationally positioned 180 degrees out of phase with respect to rotation about a common optical axis, as shown in FIG. 1.) to optically couple properly.
As noted in U.S. Pat. No. 7,567,743, the entire disclosure of which is hereby incorporated herein by reference, if there is even slight rotational misalignment (e.g., up to 15 degrees of angular rotation about a common optical axis from the 180 degrees out-of-phase position), the angled end faces of the launch and receive fibers will physically interfere and create a longitudinal gap between two fibers. Thus, conventional wisdom holds that to properly terminate an angle cleaved fiber in the field, it must be cleaved in the same manner (e.g., at the same angle) as the mating fiber and be precisely rotationally aligned with the mating fiber.
Keeping the fibers/ferrules properly oriented rotationally is complicated by the fact that the angle of the cleave cannot be perceived by the naked eye. Accordingly, to avoid rotational misalignment, complex and relatively expensive tools and techniques were developed. By way of example, U.S. Pat. No. 7,567,743 and U.S. Pat. App. Pub. No. 2009/0180742, the entire disclosures of which are hereby incorporated herein by reference, disclose devices for precisely rotationally aligning, and mating in complementary fashion, fibers having matching angled cleaves.
Therefore, an approach is needed for simplifying mating of angle cleaved fibers that eliminates the need for such complex tools and techniques, and that ensures a connection or splice providing return loss/reflectance within an acceptable range. The present invention fulfills this need among others.